This invention relates to communications systems for providing announcements at locations served by a conveying system to indicate the status of a moveable conveyance of the system and in particular has application to an elevator indicator system for providing visible and/or audible announcements at landings served by the elevator as to the status of an elevator car.
It is known to provide visible indicators at landings of a building provided with an elevator in order to indicate to a user the current status of an elevator car, typically a numerical display indicating the current position of the car by reference to the number of the landing at which it is positioned. Additional announcements are also known to be provided by means of an audible gong indicating the arrival or departure of a car from a particular landing and the provision of a visible hall lantern which illuminates to indicate an up or down arrow indicating the direction of travel of the car.
The control of such announcement devices is generally effected by means of a master control unit located at a control station where the operation of the car is also controlled. Communication between the master control unit and each of the announcement devices in many installations entails a wiring loom installed in an elevator shaft in which the car operates, the wiring loom having a large number of conductors with a respective set of conductors provided for each announcement device. Where an announcement device provides a visible indication of the current position of the car, a known system provides a separate lamp to be selectively illuminated for each of the characters of an alphanumerical display corresponding to the possible car positions and for each lamp to require separate conductors to energise the lamp. Such multiple lamp display greatly increase the number of conductors required in the wiring loom.
Recent improvements have resulted in the use of LED dot matrix displays for alphanumeric announcements using a matrix of lights which can be controlled by a driving circuit in respect to serially encoded data, thereby significantly reducing the number of conductors and hence simplifying the wiring loom.
A problem still remains in that such existing systems require a minimum of three conductors to power and control the driving circuit.